Intelligent data terminals, e.g. PCs and PDAs, are increasingly used for voice communication in modern communication systems, with said data terminals being linked by means of VoIP for example.
Packet-based communication using VoIP and the associated deployment of what are known as VoIP Codecs has undesirable effects on voice quality. For example average to fairly long transit times can be expected during signal transmission, resulting in audible echoes. Also with packet-based communication, it is necessary to take into account reflections, the transit times of which are often longer and the attenuation of which is lower than that found in a natural environment. Therefore measures have to be implemented to suppress disruptive echoes, preferably by using echo cancellers in the data terminals.
Echo cancellers are based on current standards, e.g. ITU-T G.168 (2002), where for example gateway interfaces to the conventional telephone network are discussed. Alternatively ITU-T G.165 (1993) can be used for VoIP terminals, whereby this specifies significantly less stringent parameters relating to echo dispersion and required suppression than is the case with conventional telephony standards.
If the data terminals themselves are configured as VoIP terminals, they have the disadvantages of longer transit times during signal transmission and lack of echo cancellers compared with dedicated VoIP terminals. The lack of canceller in particular means that headsets have to be used for packet-based communication of this nature.
However conventional binaural headphones result in a rather un-natural hearing event, as the sound is no longer influenced by the head and the outer ear. In the case of natural hearing both ears receive the signals from all sound sources, so that time delays, level differences and tone differences create a spatial hearing experience. Tests on directional perception of incoming sound show that interaural transit time and level differences are only relevant in relation to a horizontal plane of symmetry of the head, so the direction of the incoming sound can be determined here. No time delays or level differences occur in respect of a vertical plane of symmetry of the head but the direction of the incoming sound is perceived here by means of tone differences. Three-dimensional hearing is important for spatial orientation, the differentiation of different sound sources (see Blauert, Jens (June 1997): Spatial Hearing, MIT Press, ch. 5.3) and the suppression of reflection perception (ibid, ch. 5.4). As the sound sources are located directly at the ears when headphones are used, three-dimensional hearing is prevented. The right ear only receives the signals from the right speaker, while the left ear only receives the signals from the left speaker.